11 Cell Adaptations Flashcards
What is aplasia?
Complete failure of specific tissue/organ to develop(proliferate)= embryonic developmental disorder
What would thymic aplasia result in?
Infections and autoimmune problems
What molecules regulate normal cell proliferation? (in general terms)
Proto-oncogenes
What are the 4 main phases of the cell cycle?
G1-S-G2-M
What happens at G0 of the cell cycle?
After M- cell undergoes terminal differentiation- permanent exit from cell cycle
How does the body increase the growth of a tissue?
-Shortening cell cycle -Converting quiescent cells (retained ability to divide)- proliferating cells
What happens during G1?
Cell grows
What happens during S phase?
DNA synthesis
What happens during G2 phase?
Cell prepares to divide (e.g. protein synthesis
What is the Restriction (R) Point?
At end of G1- Critical checkpoint (for DNA damage)
How many checkpoints are there in the cell cycle?
3
What is the p53 protein?
If checkpoint activation occurs- protein suspends cell cycle-triggers DNA repair mechanisms/apoptosis
Apart from the R Point, where are the other 2 major checkpoints in the cell cycle?
G1/S and G2/M
What are the proteins which regulate the cell cycle?
Cyclins CDKs CDK inhibitors
How do activated CDKs drive the cell cycle?
Phosphorylating proteins
What is the main protein which gets phosphorylated to drive the cell cycle?
Retinoblastoma Susceptibility Protein (RB Protein)
How do growth factors have an affect on the cell cycle?
-Stimulating cyclin production -Inhibiting production of CDK inhibitors
Define ‘Cell Adaptation’
State between normal unstressed cell and overstressed injured cell
What is Hyperplasia?
Increase in cell number (increasing tissue and organ size)
What may cause cell hyperplasia? (in general terms)
1-Increased functional demand (e.g. stimulated hormonally) 2-External Stimulation (Stimulated by damage=compensatory)
In what type of cell populations does hyperplasia occur?
Labile Stable
Is hyperplasia reversible?
Yes ( it is under physiological control)
How is hyperplasia different from regeneration?
Leads to increase in cell number
What might cause pathological hyperplasia?
1-Excessive hormonal stimulation 2-Excessive GF production
Why is neoplasia a risk in hyperplastic tissue?
Repeated cell divisions- increases risk of mutations
Give an example of physiological hyperplasia.
-Increased bone marrow due to hypoxia- increased erythropoietin -Proliferation of endometrium due to oestrogen
Give an example of pathological hyperplasia.
-Epidermal thickening due to chronic eczema -Enlargement of thyroid gland- iodine deficiency
What is Hypertrophy?
Increase in cell size (increasing tissue and organ size)
In which cell population is cell hypertrophy usually seen?
Permanent cell population (limited replicative potential)
What may cause hypertrophy? (in general terms)
1-Increased functional demand 2-Hormonal stimulation
What is the usual stimulus for a combination of hypertrophy and hyperplasia to occur?
Endocrine stimulation
Give an example of physiological hypertrophy.
1- Skeletal muscle (body builder) 2-Smooth muscle- pregnant uterus (under oestrogen influence)
Give an example of pathological hypertrophy.
1-Ventricular cardiac muscle hypertrophy (due to hypertension/valvular disease) 2-Smooth muscle hypertrophy- intestinal stenosis
How do hypertrophy and hyperplasia differ from neoplasia?
Cells/tissues return to normal size when stimulus removed in hypertrophy/hyperplasia
What is ‘atrophy’?
Shrinkage in cell size (cell atrophy) (reduces its function) Shrinkage in cell number (tissue atrophy) (at point where survival=still possible)
What causes atrophy (in general terms)?
1-Reduced GF supply 2-Reduced nutrient supply
In organs undergoing atrophy, which cell type will go first?
Parenchymal stem cells before stromal cells (so often lots of CT in atrophic organs)
Give an example of where atrophy can be linked with senescence.
Atrophy of hair follicles- baldness
Is atrophy reversible?
Up to a point in some cases (less so when parenchymal cells = replaced by CT)
What’s the best way to treat atrophy?
Remove the cause
Give an example of physiological atrophy.
-Ovarian atrophy- post menopause - Decreased uterus size- after parturition
Give an example of causes of pathological atrophy.
-Reduced functional demand e.g. muscle disuse in a cast -Loss of innervation (motor nerve) -Inadequate blood supply (prolonged)= tissue death -Inadequate nutrition -Loss of endocrine stimulation -Persistent injury- e.g. polymyositis -Senile atrophy -Pressure e.g. tissues around benign tumour e.g. cerebral -Occlusion of secretory duct e.g. in pancreas -Toxic agents/drugs e.g. bone marrow -X-rays -Immunological mechanisms
What is metaplasia?
Reversible replacement of one adult differentiated cell by another. (expression of new genetic programme)
In what types of cells does metaplasia occur?
Varieties of: -Epithelia -Connective Tissue Only in populations that CAN REPLICATE
In general terms, why does metaplasia occur?
Change one type of cell to another more suited to altered environment. (e.g. columnar epithelium–> squamous epithelium
How does metaplasia differ from dysplasia?
Metaplasia- cells= fully differentiated Dysplasia- cells= disorganised + abnormal differentiation BUT metaplasia= sometimes prelude to dysplasia/cancer
Give an example in which metaplasia can be useful.
Bone marrow destroyed due to disease- splenic tissue to bone marrow
Give an example of pathological metaplasia.
Cigarette smoke- columnar epithelium–>stratified squamous epithelium. Lacks mucociliary escalator.
What is ‘Barrett’s oesophagus’?
Flat, non-secreting epithelia=replaced by secretory epithelium/glands w./ persistent acid reflux
What is ‘Traumatic myositis ossificans’?
Fibroblasts in muscle tissue change to osteoblast- after trauma- metaplastic bone develops in muscle
What is hypoplasia?
Congenital underdevelopment/incomplete development of tissue/organ (inadequate cell number) =(spectrum w./ aplasia)
What is atresia?
‘No orifice’ - congenital imperforation of opening e.g. anus/vagina
How is regeneration different from reconstitution?
Reconsitution= replacement of lost body part rather than small group of cells
What is ‘Involution’?
Normal, programmed shrinkage of organ (overlaps w./ atrophy)
Give an example of involution occurring in the body.
-Uterus after child birth
What is dysplasia?
Abnormal maturation of cells in tissue- often pre-cancerous condition
